Residual Layer Thickness Measurement and Correction

ABSTRACT

In nano-imprint lithography it is important to detect thickness non-uniformity of a residual layer formed on a substrate. Such non-uniformity is compensated such that a uniform residual layer may be formed. Compensation is performed by calculating a corrected fluid drop pattern.

This application for patent claims priority to U.S. Provisional Patent Application Ser. No. 60/788,808, which is hereby incorporated by reference herein.

BACKGROUND

Nano-fabrication involves the fabrication of very small structures, e.g., having features on the order of nanometers or smaller. One area in which nano-fabrication has had a sizeable impact is in the processing of integrated circuits. As the semiconductor processing industry continues to strive for larger production yields while increasing the circuits per unit area formed on a substrate, nano-fabrication becomes increasingly important. Nano-fabrication provides greater process control while allowing increased reduction of the minimum feature dimension of the structures formed. Other areas of development in which nano-fabrication has been employed include biotechnology, optical technology, mechanical systems and the like.

An exemplary nano-fabrication technique is commonly referred to as imprint lithography. Exemplary imprint lithography processes are described in detail in numerous publications, such as United States patent application publication 2004/0065976 filed as U.S. patent application Ser. No. 10/264,960, entitled, “Method and a Mold to Arrange Features on a Substrate to Replicate Features having Minimal Dimensional Variability”; United States patent application publication 2004/0065252 filed as U.S. patent application Ser. No. 10/264,926, entitled “Method of Forming a Layer on a Substrate to Facilitate Fabrication of Metrology Standards”; and U.S. Pat. No. 6,936,194, entitled “Functional Patterning Material for Imprint Lithography Processes,” all of which are assigned to the assignee of the present invention.

Imprint lithography disclosed in each of the aforementioned United States patent application publications and United States patent includes formation of a relief pattern in a polymerizable layer and transferring a pattern corresponding to the relief pattern into an underlying substrate. The substrate may be positioned upon a motion stage to obtain a desired position to facilitate patterning thereof. To that end, a template is employed spaced-apart from the substrate with a formable liquid present between the template and the substrate. The liquid is solidified to form a solidified layer that has a pattern recorded therein that is conforming to a shape of the surface of the template in contact with the liquid. The template is then separated from the solidified layer such that the template and the substrate are spaced-apart. The substrate and the solidified layer are then subjected to processes to transfer, into the substrate, a relief image that corresponds to the pattern in the solidified layer.

The solidified layer may comprise a residual layer of material, i.e., a contiguous layer. Residual layer thickness (RLT) and residual layer thickness uniformity are key metrics for evaluating the quality of imprinted wafers. For many applications, a plasma etch step directly follows imprinting. Film thickness uniformity requirements for plasma etching are well known in the field. RLT uniformity determines the film thickness uniformity of imprinted samples to be etched. Presently, residual layer thickness uniformity is evaluated using the unaided eye to look at fringe patterns. To that end, there is no quantitative feedback to improve the residual layer uniformity once the liquid is positioned between the template and the substrate.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a simplified side view of a lithographic system having a template spaced-apart from a substrate;

FIG. 2 illustrates a residual layer;

FIG. 3 is a simplified elevation view of a film thickness measurement tool proximate the substrate, shown in FIG. 1;

FIG. 4 illustrates an image taken by the thickness measurement tool, shown in FIG. 3;

FIG. 5 is simplified three dimensional representation of the image, shown in FIG. 4;

FIG. 6 is a top down view of the substrate having a drop pattern positioned thereon;

FIGS. 7A-7D illustrate exemplary steps for addressing a non-uniform residual layer; and

FIG. 8 illustrates a process for compensating for a non-uniform residual layer.

DETAILED DESCRIPTION

Referring to FIG. 1, a system 8 to form a relief pattern on a substrate 12 includes a stage 10 upon which substrate 12 is supported and a template 14, having a patterning surface 18 thereon. In a further embodiment, substrate 12 may be coupled to a substrate chuck (not shown), the substrate chuck (not shown) being any chuck including, but not limited to, vacuum and electromagnetic.

Template 14 and/or mold 16 may be formed from such materials including but not limited to, fused-silica, quartz, silicon, organic polymers, siloxane polymers, borosilicate glass, fluorocarbon polymers, metal, and hardened sapphire. As shown, patterning surface 18 comprises features defined by a plurality of spaced-apart recesses 17 and protrusions 19. However, in a further embodiment, patterning surface 18 may be substantially smooth and/or planar. Patterning surface 18 may define an original pattern that forms the basis of a pattern to be formed on substrate 12.

Template 14 may be coupled to an imprint head 20 to facilitate movement of template 14, and therefore, mold 16. In a further embodiment, template 14 may be coupled to a template chuck (not shown), the template chuck (not shown) being any chuck including, but not limited to, vacuum and electromagnetic. A fluid dispense system 22 is coupled to be selectively placed in fluid communication with substrate 12 so as to deposit polymeric material 24 thereon. It should be understood that polymeric material 24 may be deposited using any known technique, e.g., drop dispense, spin-coating, dip coating, chemical vapor deposition (CVD), physical vapor deposition (PVD), and the like.

A source 26 of energy 28 is coupled to direct energy 28 along a path 30. Imprint head 20 and stage 10 are configured to arrange mold 16 and substrate 12, respectively, to be in superimposition and disposed in path 30. Either imprint head 20, stage 10, or both vary a distance between mold 16 and substrate 12 to define a desired volume therebetween that is filled by polymeric material 24.

Referring to FIGS. 1 and 2, typically, polymeric material 24 is disposed upon substrate 12 before the desired volume is defined between mold 16 and substrate 12. However, polymeric material 24 may fill the volume after the desired volume has been obtained. After the desired volume is filled with polymeric material 24, source 26 produces energy 28, e.g., broadband energy that causes polymeric material 24 to solidify and/or cross-link conforming to the shape of a surface 25 of substrate 12 and patterning surface 18, defining a patterned layer 50 on substrate 12 having a contiguous formation of polymeric material 24 over surface 25. More specifically, patterned layer 50 comprises sub-portions 34 a and 34 b, with sub-portions 34 b being in superimposition with protrusions 19, with sub-portions 34 a having a thickness t1 and sub-portions 34 b having a thickness t2, with sub-portions 34 b commonly referred to as the residual layer. Thicknesses t1 and t2 may be any thickness desired, dependent upon the application.

Referring to FIGS. 1, 2, and 3, the broadband energy may comprise an actinic component including, but not limited to, ultraviolet wavelengths, thermal energy, electromagnetic energy, visible light and the like. The actinic component employed is known to one skilled in the art and typically depends on the material from which imprinting layer 12 is formed. Control of this process is regulated by a processor 32 that is in data communication with stage 10, imprint head 20, fluid dispense system 22, source 26, operating on a computer readable program stored in memory 34. System 8 may further include a film thickness measurement tool 60 coupled with the substrate chuck (not shown), described further below. Film thickness measurement tool 60 may comprise an optical detection system, and further may be in data communication with processor 32. Film thickness measurement tool 60 may be a stand alone tool commonly used in semiconductor fabrication. Such tools are commercially available from Metrosol, Inc., Filmetrics, Rudolph Technologies, and J. A. Woolam.

Patterned layer 50 may have variations among thicknesses t2, which may be undesirable. More specifically, minimizing, if not preventing, variations among sub-portions 34 b, and thus, the residual layer may result in improved control of the critical dimension of pattered layer 50, which may be desired. In an example, it may be desirable to reduce variations among sub-portions 34 b below the approximately 30 nm level seen in typical imprints in order to minimize, if not prevent, the impact to etched feature critical dimension.

To that end, variations in thicknesses t2 of sub-portions 34 b may be measured generating measured data, with the measured data facilitating a design in positioning of polymeric material 24 upon substrate 12. In the present embodiment, polymeric material 24 is positioned as a plurality of droplets upon substrate 12, and thus, the measured data facilitates a design in the drop pattern of polymeric material 24. As a result, uniformity in thicknesses t2 of the sub-portions 34 b may be achieved.

The variations in thicknesses t2 of sub-portions 34 b may be measured at a plurality of points employing film thickness measurement tool 60, with the optical detection system digitizing imprinted fields, i.e., patterned layer 50, and subsequently employing processor 32 operating on a computer readable program stored in memory 34 to analyze said imprinted fields to construct a map of the thickness t2 of sub-portions 34 b across patterned layer 50. To that end, the drop pattern of polymeric material 24 may be varied, i.e., droplets may be added or subtracted, the drop offset may be varied, individual drop volumes of the plurality of drops, based upon the variations in thickness t2 of sub-portions 34 b to generate a drop pattern that may facilitate patterned layer 50 comprising sub-portions 34 b having a desired thickness uniformity.

Referring to FIGS. 1 and 3, to that end, film thickness measurement tool 60 may be positioned at a fixed angle and distance from substrate 12, with the distance from the imprint field, i.e., patterned layer 50, to film thickness measurement tool 60 being calculated. A calibration process may be required to obtain accurate dimensions of the imprint field. An alternative method for measuring the residual layer thickness measures the optical properties of the film, such as reflected intensity versus wavelength or circular versus elliptical polarization of light reflected from the field. These spectroscopic measurements are then fit to a model of the film stack to determine parameters of interest such as film thickness. Such a process can be implemented using the commercially available film thickness measurement tools noted above.

Referring to FIGS. 1 and 4, after an image of the imprint field is taken by film thickness measurement tool 60, processor 32 operating on a computer readable program stored in memory 34 may employ an algorithm to convert the image into a square (or, rectangle, circular, etc.) imprint area. Subsequently, processor 32 may convert differences in color and shade grades into a Z-height profile of the imprint field. FIG. 5 shows an example of a three-dimensional representation of the field shown in FIG. 4. Furthermore, the computer readable program stored in memory 34 may comprise a program entitled ImageJ available from http://rsb.info.nih.gov/ij/.

Further analysis of the imprinted filed is performed to map surface 25 of substrate 12 with a polynomial two-dimensional function, f(x,y). In this way, we can assign a specific thickness to each (x,y) point. Further, an average g(x,y) may be calculated, as well as deviation from this average: w(x,y)=g(x,y)−f(x,y).

The slope g(x,y) will be used to calculate the offsets in X and Y directions of the drop pattern. Deviation function w(x,y) will be used to control local unit fluid volume; number of drops, position of drops and drop volume itself.

FIG. 6 shows an exemplary drop pattern of polymeric material 24 used for imprinting that produced a desired thickness profile shown on FIG. 5. Using a multi-nozzle dispensing unit, various drop patterns can be generated on the substrate, such as a uniform grid superimposed with localized compensating drops.

Furthermore, the drop pattern on FIG. 6 corresponds to the following drop matrix, M(x,y):

-   1: (0,0) 3.3113E-4 uL (microliters)×29 drops (0,0) refers to the     center of the template -   2: (−0.95, 0.95) 3.3113E-4 uL×6 -   3: (−0.65, 0.95) 3.3113E-4 uL×15 -   4: (−0.95, 0.65) 3.3113E-4 uL×6 -   5: (−0.73, 0.73) 3.3113E-4 uL×15 -   6: (−0.56, 0.56) 3.3113E-4 uL×16 -   7: (−0.4, 0.4) 3.3113E-4 uL×13 -   8: (−0.24, 0.26) 3.3113E-4 uL×6 -   9: (0, 0.32) 3.3113E-4 uL×6 -   10: (0, 0.52) 3.3113E-4 uL×13 -   11: (−0.15, 1) 3.3113E-4 uL×7 -   12: (0, 0.8) 3.3113E-4 uL×20 -   13: (0.15, 1) 3.3113E-4 uL×7 -   14: (0.65, 0.95) 3.3113E-4 uL×15 -   15: (0.95, 0.95) 3.3113E-4 uL×6 -   16: (0.95, 0.65) 3.3113E-4 uL×6 -   17: (0.73, 0.73) 3.3113E-4 uL×15 -   18: (0.56, 0.56) 3.3113E-4 uL×13 -   19: (0.4, 0.4) 3.3113E-4 uL×13 -   20: (0.24, 0.26) 3.3113E-4 uL×6 -   21: (0.3, 0) 3.3113E-4 uL×6 -   22: (0.5, 0) 3.3113E-4 uL×13 -   23: (1, 0.15) 3.3113E-4 uL×7 -   24: (0.8, 0) 3.3113E-4 uL×15 -   25: (1, −0.15) 3.3113E-4 uL×7 -   26: (0.95, −0.65) 3.3113E-4 uL×6 -   27: (0.95, −0.95) 3.3113E-4 uL×6 -   28: (0.65, −0.95) 3.3113E-4 uL×10 -   29: (0.73, −0.73) 3.3113E-4 uL×15 -   30: (0.56, −0.56) 3.3113E-4 uL×13 -   31: (0.4, −0.4) 3.3113E-4 uL×13 -   32: (0.24, −0.26) 3.3113E-4 uL×6 -   33: (0, −0.32) 3.3113E-4 uL×6 -   34: (0, −0.52) 3.3113E-4 uL×13 -   35: (0.15, −1) 3.3113E-4 uL×7 -   36: (0, −0.8) 3.3113E-4 uL×15 -   37: (−0.15, −1) 3.3113E-4 uL×7 -   38: (−0.24, −0.26) 3.3113E-4 uL×6 -   39: (−0.4, −0.4) 3.3113E-4 uL×13 -   40: (−0.56, −0.56) 3.3113E-4 uL×19 -   41: (−0.73, −0.73) 3.3113E-4 uL×15 -   42: (−0.65, −0.95) 3.3113E-4 uL×10 -   43: (−0.95, −0.95) 3.3113E-4 uL×6 -   44: (−0.95, −0.65) 3.3113E-4 uL×6 -   45: (−1, −0.15) 3.3113E-4 uL×7 -   46: (−0.8, 0) 3.3113E-4 uL×20 -   47: (−1, 0.15) 3.3113E-4 uL×7 -   48: (−0.5, 0) 3.3113E-4 uL×13 -   49: (−0.3, 0) 3.3113E-4 uL×6

To that end, to compensate for variations among thicknesses t2 of sub-portions 34 b, the following may be employed:

-   -   1. Use function g(x,y) to calculate drop pattern offset         represented as a vector S:         S−Agrad(g(x,y))i−Bgrad(g(x,y))j,     -    where i and j are the unit vectors along X and Y axes. A, B are         the proportionality coefficients that need to be determined         experimentally, for instance, using a blank mesa template.         Imprint new field and measure g(x,y) again. Verify that the         slope in X and Y is near zero.     -   2. After gradient of function g(x,y) is minimized, individual         drop volumes are addressed. Multiply the drop pattern matrix         M(x,y) by function w′(x,y), where:         w′(x,y)=w(x,y)/(max(w(x,y))−min(w(x,y)))     -   So new drop pattern M′(x,y) will be:         M′(x,y)=M(x,y)*w′(x,y)     -   3. Verify that the new imprint has uniform thickness by         measuring the slope of g(x,y) and minimizing function w(x,y).

A process for obtaining a uniform residual layer thickness (RLT) is illustrated in FIGS. 7A-7D and 8. In step 801, the imprint tool is calibrated to determine how much fluid to dispense to make an imprint with a desired thickness. In step 802, a uniform distribution of fluid is deposited on the substrate as illustrated in FIG. 7A. An imprint is performed. Evaporation and other non-uniformities may cause the RLT to be non-uniform. In step 803, RLT uniformity is measured across a dense array of points in the imprinted field using the film thickness measurement tool 60. In step 804, if a desired uniformity is achieved, then the process may end in step 805. If not (see FIG. 7B), then the process proceeds to step 806, where one of the above algorithms is employed, such as in software running in processor 32, to calculate a new corrected drop pattern, which will add drops, or increase drop size, to thin areas and/or remove drops, or decrease drop size, from thick areas to achieve improved RLT uniformity. The process then returns to step 802 to make a new imprint using the corrected drop pattern (see FIG. 7C), and steps 803 and 804 are performed again. This process may be repeated as needed until a desired uniformity RLT is achieved, as illustrated in FIG. 7D.

This above-mentioned method may be employed to obtain a desired volume of polymeric fluid 24 positioned upon substrate 12 to the volume of features (protrusions 17 and recesses 19) in mold 16. In a further embodiment, the above-mentioned method may be employed to compensate for evaporation in the plurality of droplets of polymeric material 24 after positioning the same upon substrate 12 and prior to contact with mold 16. In both cases, matching a volume of polymeric material 24 upon substrate 12 to the volume of features in mold 16 result in improved residual layer uniformity, i.e., variations among thicknesses t2 of sub-portions 34 b. This improved residual layer uniformity enables better control of feature CDs across imprinted and etched wafers. Furthermore, the above-mentioned may also minimize, if not reduce, and impact of faceting during a breakthrough etch of the residual layer.

The embodiments of the present invention described above are exemplary. Many changes and modifications may be made to the disclosure recited above, while remaining within the scope of the invention. Therefore, the scope of the invention should not be limited by the above description, but instead should be determined with reference to the appended claims along with their full scope of equivalents. 

1. In an imprint lithography system, a method comprising: a) depositing a plurality of drops of imprint fluid on a substrate, the plurality of drops having a drop pattern in which each of the plurality of drops has an assigned size and position on the substrate; b) performing an imprint of the plurality of drops of imprint fluid by patterning the imprint fluid between a mold and the substrate resulting in an imprinted layer; c) measuring a thickness of a residual layer of the imprinted layer; d) calculating a new drop pattern that compensates for nonuniformities in the thickness of the residual layer by adjusting the assigned size and position of certain ones of the plurality of drops; and e) repeating step b).
 2. The method as recited in claim 1, further comprising repeating step c) after step e).
 3. The method as recited in claim 2, wherein steps b), c), and d) are repeated until a desired uniformity of the thickness of the residual layer is achieved.
 4. An imprint lithography system, comprising: a fluid dispense system for depositing a plurality of drops of imprint fluid on a substrate, the plurality of drops having a drop pattern in which each of the plurality of drops has an assigned size and position on the substrate; an imprint mold for performing an imprint of the plurality of drops of imprint fluid by patterning the imprint fluid between the imprint mold and the substrate resulting in an imprinted layer; a film thickness measurement tool for measuring a thickness of a residual layer of the imprinted layer; circuitry for calculating a new drop pattern that compensates for nonuniformities in the thickness of the residual layer by adjusting the assigned size and position of certain ones of the plurality of drops. 